1. Field of the Invention
The present invention relates to a printing apparatus such as an inkjet printer and a method for printing an image.
2. Description of the Related Art
Conventional printing apparatus such as a serial inkjet printer includes those which detect a rear end of a printing medium and print an image in a remaining region from a printing position of a print head up to the rear end of the printing medium after detecting the rear end. Specifically, when the printing apparatus of this type detects the rear end of the printing medium, in order to use only print data corresponding to the remaining region from the printing position of the print head up to the rear end of the printing medium, print data in the excess of the remaining region is discarded. In general, the printing apparatus of this type includes a swing-type detection lever for the printing medium and an optical sensor for detecting the operation of the detection lever as means for detecting the rear end of the printing medium.
In such a printing apparatus, the detection lever is provided on a transport path for the printing medium and upstream of the print head at a predetermined distance from the same. The detection lever starts swinging when it is put in contact with a front end of the printing medium being transported and returns to an initial position (standby position) when the rear end of the printing medium passes through the same. The sensor detects the detection lever of that returns to the standby position after the rear end of the printing medium passes therethrough and outputs a signal indicating that the rear end of the printing medium has been detected.
In such a mechanical detecting means for the printing medium, a certain delay associated with the swing of the detection lever occurs when the rear end of the printing medium is detected regardless of the velocity at which the printing medium is transported. Therefore, the remaining region of the printing medium as described above has been corrected by a constant value according to the delay associated with the detection lever.
In printing apparatus as described above, it is becoming common to increase the transportation velocity of the printing medium when a marginal space of the printing medium is forwarded in order to improve throughput. When the transportation velocity of the printing medium is thus changed during a series of printing operations, the remaining region as described above also changes in accordance with the velocity of the printing medium transportation. For the purpose of controlling the remaining region of the printing medium accurately, it is therefore insufficient to correct the remaining region of the printing medium using only the constant value according to the delay attributable to the detection lever.
The printing apparatus disclosed in Japanese Patent Application Laid-open No. 10-058801 (1998) is known as a technique taking such a change in the transportation velocity of the printing medium into consideration. In the printing apparatus disclosed in the publication, the remaining region from a printing position of a print head up to a rear end of a printing medium is controlled in accordance with the velocity at which the printing medium is transported. Specifically, in the printing apparatus, a length D of the remaining region for a low transportation velocity is stored in advance, and the length D of the remaining region is corrected by a predetermined value α to set the length of the remaining region as (D-α) when the velocity of the printing medium transportation increases beyond the low transportation velocity.
However, the printing apparatus disclosed in Japanese Patent Application Laid-open No. 10-058801 (1998) merely corrects the length of the remaining region by the constant value α in accordance with the velocity of the printing medium transportation, although the change in the transportation velocity of the printing medium is taken into consideration to some degree indeed. Therefore, the technique disclosed in the publication does not sufficiently mitigate problems such as a positional shift of an image and ejection of ink on to objects other than the printing medium such as a platen.
The present invention is directed to overcome one or more of the problems as set forth above.